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Question about "760: LSN data from server is blank." message

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JMilnes



Joined: 03 Sep 2009
Posts: 1

PostPosted: Thu Sep 03, 2009 3:58 pm    Post subject: Question about "760: LSN data from server is blank." message Reply with quote

I have been seeing "760: LSN data from server is blank." showing up in a report I run to check the status of my backups. Its not a regular thing but every few days I will have a transaction log backup fail with that message. When this happens to a differential or full backup I have the job set up to automatically schedule a new backup and that works fine. How ever with the transaction log backups these errors mess with some log shipping I have set up.

In the transaction log backup job I run, I have it set up to move the file to another location when it finishes the backup. When I get one of these errors the file is not moved. So since my log shipping job pulls the file from this secondary location it will fail, it attempts to apply the transaction log that occurs after the missing file and then that will fail with
Quote:
"SQL error 4305: The log in this backup set begins at LSN 151107000002399800001, which is too late to apply to the database. An earlier log backup that includes LSN 151102000000755100001 can be restored"
Easy fix, I just move the missing file over and kick off my restore job.

But this is where i am a bit confused, this is the file that generated the "760: LSN data from server is blank." error when it was taken. I run "restore sqbheaderonly" and I can see that it is in fact missing the LSN information. But this still restores. I am curious as to why this restores with out errors, and if I should really be doing something different, instead of just applying that transaction log.
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petey



Joined: 24 Apr 2005
Posts: 2299

PostPosted: Sat Sep 05, 2009 4:18 pm    Post subject: Reply with quote

In each backup file that SQL Backup creates, it stores the LSN details of that backup in the SQL Backup header (the first 1024 bytes) of that file. As you rightly pointed out, this information is only critical for the batch SQL Backup transaction log restores.

The LSN details stored in the backup data as generated by SQL Server is always present, thus you can still restore the transaction log. You can verify this by running the SQL Backup RESTORE HEADERONLY command.

As to the source of the error, it's being generated because SQL Backup failed to retrieve the LSN details from the msdb tables. Could you please try querying the backup history tables, to see if you can retrieve the LSN details for the backups that raised error 760? E.g.

Code:
SELECT a.backup_start_date, a.backup_finish_date, a.first_lsn, a.last_lsn FROM msdb..backupset a
INNER JOIN msdb..backupmediafamily b ON a.media_set_id = b.media_set_id
WHERE b.physical_device_name = <backup file name>

Thanks.
_________________
Peter Yeoh
SQL Backup Consultant Developer
Associate, Yohz Software
Beyond compression - SQL Backup goodies under the hood, updated for version 7
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